Modern mobile telecommunications standards continue to demand increasingly greater rates of data exchange (data rates). One way to achieve a high data rate in a mobile device is through the use of carrier aggregation. Carrier aggregation allows a mobile device to aggregate bandwidth across one or more operating bands in the wireless spectrum. The increased bandwidth achieved as a result of carrier aggregation allows a mobile device to obtain higher data rates than have previously been available.
FIG. 1 is a table describing a number of wireless operating bands in the wireless spectrum. One or more of the wireless operating bands may be used, for example, in a code division multiple access (CDMA), global system for mobile communications (GSM), long term evolution (LTE), or LTE-advanced equipped mobile device. The first column indicates the operating band number for each one of the operating bands. The second and third columns indicate the uplink and downlink frequency bands for each one of the operating bands, respectively. Finally, the fourth column indicates the duplex mode for each one of the operating bands. In non-carrier aggregation configurations, a mobile device will generally communicate using a single portion of the uplink or downlink frequency bands within a single operating band. In carrier aggregation applications, however, a mobile device may aggregate bandwidth across a single operating band or multiple operating bands in order to increase the data rate of the device.
FIG. 2A is a diagram illustrating a conventional, non-carrier aggregation configuration for a mobile device. In the conventional configuration, a mobile device communicates using a single portion (e.g., a resource block in LTE terminology) of a wireless spectrum 10 within a single operating band 12. Under the conventional approach, the data rate of the mobile device is constrained by the limited available bandwidth.
FIGS. 2B-2D are diagrams illustrating a variety of carrier aggregation configurations for a mobile device. FIG. 2B shows an example of contiguous, intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 14A and 14B are located directly adjacent to one another and are in the same operating band 16. FIG. 2C shows an example of non-contiguous intra-band carrier aggregation, in which the aggregated portions of the wireless spectrum 18A and 18B are located within the same operating band 20, but are not directly adjacent to one another. Finally, FIG. 2D shows an example of inter-band carrier aggregation, in which a first portion of the wireless spectrum 22A is located in a first operating band 24 and a second portion of the wireless spectrum 22B is located in a second operating band 26. It is advantageous for a mobile device to support each one of the previously described carrier aggregation configurations.
The use of carrier aggregation may pose unique problems for the front end and/or RF amplification circuitry in a mobile device. For instance, certain carrier aggregation configurations may require specialized hardware and/or software to implement.
In addition to greater data rates, consumer demand for longer battery life from mobile devices has resulted in the development of many power-saving techniques. One way to conserve power in a mobile device is through the use of envelope tracking. Envelope tracking involves modulating a supply voltage provided to an amplifier based on the instantaneous magnitude (i.e., the envelope) of an RF input signal provided to the amplifier. FIG. 3 illustrates the basics of envelope tracking. Specifically, FIG. 3 shows an amplitude-modulated RF signal 28. Conventionally, a constant supply voltage at a level sufficient to ensure adequate headroom across the entire amplitude (input power) range of the RF signal 28 would be supplied to an RF amplifier, as shown by line 30. This results in a significant amount of wasted energy when the amplitude of the RF carrier is low, as illustrated by line 32. Accordingly, an envelope tracking power supply signal tracks the amplitude of the RF signal 28, as illustrated by line 34, and therefore saves significant amounts of energy.
While envelope tracking has been increasingly utilized, it often requires specialized hardware to accomplish. This hardware must be capable of providing the modulated supply voltage at a frequency high enough to keep up with changes in the amplitude of the RF signal. Generally, this requires an envelope tracking power supply to be capable of operating at frequencies around two to three times that of the modulation bandwidth of the RF signal. In situations where the modulation bandwidth of the RF signal is high, for example, in non-contiguous intra-band carrier aggregation configurations, hardware limitations may make it difficult to achieve such high speeds.
Conventional approaches to the aforementioned problems have generally focused on using average power tracking during the amplification of wide modulation bandwidth RF signals. Average power tracking involves providing an unmodulated (i.e., constant) supply voltage to an RF amplifier. As mentioned above, the magnitude of a supply voltage in an average power tracking approach must be high enough to ensure adequate headroom to avoid compression of the RF signal. Accordingly, this often means that a relatively large supply voltage must be provided to the RF amplifier. The envelope power converter circuitry in an envelope power supply is generally designed to provide a large supply voltage only for short periods of time in order to increase the efficiency thereof. In other words, envelope power supplies generally are not capable of sustaining the relatively large supply voltage required by an average power tracking approach. Accordingly, an additional power supply is required to use both envelope tracking and average power tracking together, or the components of the envelope power converter circuitry must be modified to support the continuous output of a large voltage, which will generally degrade the efficiency of the supply.
In light of the above, there is a present need for an improved envelope tracking method and system capable of efficiently operating with high bandwidth RF signals.